LPM-based NLI Estimation over Heterogeneous Links: Analysis and Comparison

Accurate estimation of Non-Linear Interference (NLI) is critical for optimizing ultra-wideband optical networks. This paper investigates the performance of Longitudinal Power Monitoring (LPM)-based NLI estimation, focusing on heterogeneous links. While LPM offers robust, link-agnostic estimation of Self-Channel Interference (SCI), it requires correction for Cross-Channel Interference (XCI) to fully assess NLI. Two correction approaches are compared: a simplified Gaussian Noise (GN)-model-based approximation and the more accurate Polynomial Closed-Form GN/EGN model (PCFM). Experimental validation is conducted over both homogeneous and heterogeneous links, including scenarios with unequal channel power, on two different modulation formats. Results show that while estimation accuracy decreases in complex scenarios, LPM-based methods still provide sufficiently reliable performance for practical optimization tasks, such as determining optimal launch power. These findings support the use of LPM-based NLI estimation as a promising tool for real-time network monitoring and digital twin modeling.